A nuclear fuel rod is comprised of a column of fuel pellets sealed in an elongated cladding tube typically formed of a zirconium alloy. In the process of manufacturing nuclear fuel rods, the first major operation prior to loading the tubes with fuel pellets is to seal off one of their open ends by welding an end plug thereto in a first weld operation. In accordance with established practice, tubes are brought to a welding table where an operator utilizes equipment to mate an end plug with an open end of each of a succession of tubes. The mated items are then welded together using an inert gas-arc welder and, after the weld has cooled sufficiently, a quality assurance technician inspects the weld to determine if it meets predetermined quality control standards, including, inter alia, weld integrity and weld bead diameter. Following inspection, the welded tube is placed in the appropriate accept or reject trays, and the welding operation begins anew on the next tube. After a pre-established number of acceptable tubes have accumulated, all or a selected number thereof may be subjected to additional quality assurance tests and then transported to a fuel loading operation.
It is thus seen that this welding operation is a time consuming, labor intensive process. Human participation in the welding and quality assurance operations with respect to each first end plug weld imposes a serious bottleneck on nuclear fuel rod production. This problem is exacerbated because each end plug weld must cool in the inert gas environment of the welder to avoid undesirable oxidation of the weld. Thus, otherwise productive time is spent waiting for a weld to cool rather than welding another end plug to another tube. Furthermore, because some quality assurance inspections are made on individual tubes while at the weld table, additional delays enter the process, further reducing productivity. Moreover, if the first end plug weld is created as a flush weld, rather than a bead weld, visual inspection is an inadequate test of weld integrity.
Human participation in the welding and inspection operations also can have a detrimental effect on the fuel rod quality. As the amount of handling increases, so does the possibility of scratching the tube surfaces. Exterior surface scratches negatively impact fuel rod integrity and lifetime due to an increased likelihood of corrosion thereat; furthermore, they lack cosmetic appeal, which is important to some customers.